Not Applicable
Not Applicable
Not Applicable
The present invention relates to solenoid operated valves and particularly those attended for use on board a motor vehicle and operating from a relatively low voltage power supply.
In certain motor vehicle emissions control systems, it is necessary to energize an electrically operated valve for closure when the engine is not running in order to perform a diagnostic procedure on the vehicle fuel system. Where the valve must be maintained in the energized state and closed position for a prolonged period of time, on the order of thirty minutes or more, severe drain on the vehicle battery and can result in a battery which has insufficient charge to restart the vehicle engine.
Accordingly, it has been desired to provide a solenoid operated valve for on-board motor vehicle usage which can be energized and maintained in the energized condition for holding the valve closed for a length of time without unduly draining charge from the vehicle battery when the engine is not operating.
Presently available solenoid operated valves draw a prohibitive amount of current for such usage and thus, it has long been desired to provide a solenoid operated valve which can be maintained in the energized state at a significantly reduced current level from the initial energization current.
Heretofore, this problem has been addressed by the use of a relatively complex electronic circuit which provided a high current for a time period sufficient to cause the armature to move the desired amount, followed by a reduced current to maintain the solenoid in the energized state. The present invention solves the above-described problem with a simplified and less costly circuit.
The present invention provides a solenoid operated valve capable of energization from an on-board vehicle low voltage power supply and which, after initial energization, magnetically latches to require a substantially reduced current level to maintain the energized state and closure of the valve. The present invention thus minimizes the current draw from the vehicle power supply for diagnostic purposes when the engine is not running and recharging the battery.
The valve of the present invention has a positive temperature coefficient (PTC) resistor or thermistor connected electrically in series with the valve coil; and, upon initial energization, the thermistor has a relatively low resistance permitting substantial current flow to the coil for creating a sufficient magnetomotive force to effect valve closing. Upon heating of the thermistor from the current flow therethrough, the thermistor resistance increases to a significantly higher level resulting in reduced current flow to the solenoid coil. The initial closing of the valve effects closing of the working air gap between the armature and a pole piece in the valve; and the resultant decrease in magnetic reluctance upon closing of the air gap enables sufficient force to hold the valve closed at the reduced current level.
The present invention thus provides a solenoid operated valve suitable for use on board a vehicle for emissions diagnostic test procedures performed after the vehicle engine is shut off which minimizes the current drain on the vehicle battery to prevent battery discharge to a level which would otherwise disable restarting of the vehicle engine.